import java.util.Scanner;
public class Main3 {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            while (sc.hasNext()) {
                int sum = 0;
                int n = sc.nextInt();
                sum = func(n);
                System.out.println(sum);
            }
        }
        public static int func(int n) {
            if (n == 1 || n == 2) return n;
            return func(n - 1) + func(n - 2);
        }
}

